There is a fascinating book by Alison Milbank, on Chesterton and Tolkien as Theologians which is reviewed here. There is also an interview with the author here in which she makes the fascinating points like these:
"Tolkien says that Chestertonian fantasy shows you the actual world from a new angle but thoroughgoing fantasy is like opening a box that allows out new things and releases them from our ownership of them. This is a really philosophical statement. The Enlightenment philosopher Kant said we have no access to things in themselves, and all we have is our own perception of the world. This leads to an alienated form of knowledge. Tolkien, following Chesterton, is a realist in a philosophical sense, because he thinks that we can be aware of a world beyond our own perceptions. Paradoxically, fiction – creating your own fantasy world – is not a way of owning your own private reality but setting the things in that world free – like Tom Bombadil putting the contents of the barrow-wights’ hoard out on the hillside."